This invention relates to an improved apparatus for raising and lowering detachable gooseneck trailers between their driving and loading positions, and in particular to such an apparatus which moves smoothly and efficiently between raised and lowered positions without engaging the ground as a lifting point.
The apparatus further relates to an improved apparatus for holding a gooseneck erect on a trailer when the tractor has been disconnected. The conventional detachable gooseneck trailer is arranged so that the trailer's front end can be lowered to the ground and disconnected from the gooseneck in order to facilitate loading from the front end. This is accomplished by using a gooseneck to interconnect the trailer to the tractor, with the front end of the gooseneck which is attached to the tractor by means of a fifth wheel and its rear end is attached to the trailer by means of a hook coupling. Accordingly, when the rear end of the gooseneck is raised or lowered it also moves the front end of the trailer to a raised or lowered position.
The gooseneck is raised and lowered by means of hydraulic jacks which are attached to the gooseneck and this arrangement has not always been effective due to the fact that the jacks raise the gooseneck by having their rams extended while in contact with the ground on which the trailer rests. Since trailers of this type generally are used for transporting construction equipment, they are often used on muddy terrain or terrain which will not otherwise support the weight of the trailer on the limited area of the support pad of the hydraulic jacks. In this event the hydraulic jacks tend to sink into the ground rather than lifting the trailer.
To overcome this problem, a non-ground engaging lift system has been provided in which the hydraulic jack(s) push against the trailer instead of the ground in a loading position. The weight of the trailer is supported by the front end of the trailer. By providing a lifting system which is not required to interact with the surrounding terrain many of the shortcomings of earlier lifting apparatus were overcome. In a typical non-ground engaging system the lifting apparatus comprises extensible piston cylinders which are attached pivotably at their cylinder ends to the gooseneck. The shafts of the piston cylinders slidably contact ramps on the trailer at points defined by fore and aft stops. Thus when the shafts of the piston cylinders are extended, the points at which they are connected to the gooseneck are moved away from the points at which they contact the trailer, causing the trailer and gooseneck to rotate in opposite directions about their common pivot point at the hook coupling. The end points of the piston cylinders and the pivot point are arranged relative to one another so that as this occurs the rear end of the gooseneck and the front end of the trailer are raised. Conversely, as the piston cylinder shafts are retracted the gooseneck and trailer rotate in opposite directions about the pivot point and the front end of the trailer and the rear end of the gooseneck are lowered.
A drawback to the non-ground engaging system known in the art is that as the geometry changes by the extension or retraction of the ram and the relative positions of the pivot point, gooseneck contact point and trailer contact point, the change is accommodated by the sliding engagement of the ram on the trailer. This sliding engagement is irregular imparting shocks to the hydraulic system and is unconstrained, requiring stops or other structure to keep the sliding movement within acceptable bounds. Bending forces on the ram damaging to the system result from this uncontrolled point.